1. Field of the Invention
The present invention relates to a tear secretion quantity examination system suitable for dry-eye evaluation.
2. Description of the Related Art
Tears are secreted by a lacrimal gland situated above the ear side of the eye, form a tear layer on the cornea surface each time the eye blinks, and are discarded to the lacrimal points located at the nasal side. The tears prevent eyes from drying, sterilize and wash them, and supply nutrients thereto; they are indispensable for normal functioning of the eyes. The quantity of tears present on the eye surface is apparently determined by the balance of (1) secretion by the lacrimal gland, (2) discharge from the lacrimal points, and (3) evaporation from the eye surface. When tear secretion is too small, a dry eye condition which is called an ATD (Aqueous Tear Deficiency) is realized.
The tear secretion quantity have been conventionally evaluated by a Schirmer test in which a filtration paper was inserted between the eye and the eyelid and the wetting degree of the filtration paper was studied after 5 minutes, and the tear discharge quantity was evaluated by a clearance test in which fluorescent eye drops are dropped into the eye and the fluorescence yield of the fluorescent eye drops was observed over time. There is no established method for evaluating the tear evaporation quantity, but a method is known which uses a moisture evaporation quantity measurement unit equipped with a quarts oscillator humidity sensor in a tubular body surrounding the eye (Japanese Patent Application Laid-open No. 2001-46339).
However, the problem associated with the Schirmer test was that a filtration paper had to be inserted between the eye and the eyelid, which placed a large burden on the patient.
In the clearance test, fluorescent eye drops are dropped in the eye and after a certain time, the attenuation ratio of fluorescence was studied by using a Schirmer test paper. Therefore, a large burden was placed on the patient, similarly to the Schirmer test. Furthermore, a large fluorescence analyzer and significant space are required for measuring the fluorescence yield.
In the method using the moisture evaporation quantity measurement unit (Japanese Patent Application Laid-open No. 2001-46339), the tear evaporation quantity can be measured in a simple and non-invasive manner, and the amount of information that is obtained with respect to the tear secretion quantity or retention quantity is small.